News - 6 Common Problems with Silicone Sealants and How to Fix Them

Silicone sealants are widely used for construction, glazing, and household repairs because of their flexibility, weather resistance, and long lifespan. But even the best silicone sealant can fail if applied incorrectly or under the wrong conditions.

Below, we outline the most common problems with silicone sealants, their causes, and step-by-step solutions to fix them.

1. Poor Adhesion (Sealant Not Sticking)

Symptoms: The sealant peels away, detaches, or does not bond to the surface.

Causes:

--Dirty, dusty, or oily substrates
--Moisture on the surface during application
--Incompatible substrate (e.g., polyethylene, PTFE, or oily woods)
--Expired or low-quality sealant

How to Fix It:

1.Remove the failed sealant completely with a scraper or sealant remover.
2.Clean the substrate with solvent (IPA or acetone) to remove oils and dust.
3.Use a primer if bonding to porous materials like concrete or natural stone(ASTM C794 Adhesion Tests).
4.Reapply a fresh bead of a neutral silicone sealant for better adhesion

2. Bubbling or Voids in the Sealant

Symptoms: Air pockets, bubbles, or hollow spots appear inside the cured sealant.

Causes:

--Trapped air during application
--Excess moisture in the joint (especially in humid environments)
--Sealant applied too thickly in one pass

How to Fix It:

--Cut out and remove the bubbled sections.
--Ensure the substrate is completely dry before reapplying.
--Apply the sealant in layers if filling deep joints, using backer rods where needed(Dow Construction Sealants Guide).
--Choose a professional-grade structural silicone sealant for stability.

3. Sealant Shrinkage or Cracking

Symptoms: The sealant shrinks, pulls away from edges, or develops cracks.

Causes:

--Using a low-quality or solvent-based product that loses volume on curing
--Applying the sealant in extreme temperatures
--Incorrect joint design (too narrow, no allowance for movement)

How to Fix It:

--Remove the defective bead and reapply a low-shrinkage neutral cure silicone sealant.
--Follow recommended joint design per ISO 11600:2002 standards
--Apply within the manufacturer’s recommended temperature range (typically 5–40°C).

4. Mold and Mildew Growth

Symptoms: Black or dark stains appear, especially in bathrooms and kitchens.

Causes:

--Prolonged exposure to moisture and humidity
--Lack of ventilation in the area
--Using non-sanitary silicone in wet environments

How to Fix It:

--Cut out the moldy sealant completely (cleaning alone is not effective).
--Disinfect the area with diluted bleach or a mold cleaner.
--Reapply a sanitary silicone sealant with fungicidal additives.
--Improve ventilation to prevent future growth.

5. Sealant Not Curing or Staying Sticky

Symptoms: The silicone remains soft, tacky, or never hardens.

Causes:

--Expired product or improper storage
--Incompatible curing environment (low humidity for one-part RTV silicones)
Mixing error (in two-component silicones)

How to Fix It:

--Remove the uncured silicone completely.
--Use fresh product stored in a cool, dry place.
--For moisture-curing silicones, ensure proper humidity levels (40–70% RH).
--For two-component products, follow mixing ratios precisely(Sealant Curing Guide – BSI).

6. Sealant Pulling Away from Joints (Joint Failure)

Symptoms: Gaps form between the sealant and substrate, leaving the joint unsealed.

Causes:

--Movement in the substrate beyond the sealant’s flexibility range
--Incorrect joint design (too deep or too shallow)
--No backer rod or bond breaker tape used

How to Fix It:

--Redesign the joint according to ASTM C920-18(2024) standards

--Use a sealant with the right movement capability (+/- 25% or higher).

--Always apply sealant over a backer rod or bond breaker to prevent three-sided adhesion.

Sealant Pulling Away from Joints (Joint Failure)

Quick Troubleshooting Table

Problem	Main Cause	Fix
Poor adhesion	Dirty surface / incompatibility	Clean, prime, reapply
Bubbling/voids	Moisture / air entrapment	Dry, reapply thin layers
Shrinkage/cracking	Low-quality sealant / bad joint design	Use neutral cure, redesign joint
Mold growth	Non-sanitary sealant / humidity	Replace with sanitary silicone
Not curing	Expired product / wrong conditions	Use fresh sealant, correct curing environment
Joint failure	Excessive movement / wrong design	Redesign joint, use backer rod

Silicone sealants are among the most durable sealing solutions available—but only if applied correctly. By understanding common problems and their fixes, you can ensure longer service life, reduced maintenance, and better project performance.

At Siway Sealants, we provide high-performance silicone sealants designed to minimize these issues. Contact our technical support team for project-specific recommendations.

Q1. Why is my silicone sealant not sticking properly?

This usually happens due to surface contamination, moisture, or using the wrong sealant for the substrate. Always clean and dry the surface, use a primer if required, and choose the right neutral cure silicone sealant for sensitive materials like metal or stone.

Q2. How can I fix bubbles or voids in silicone sealant?

Bubbling often occurs if the substrate is damp or if the sealant is applied too quickly. Remove the failed section, dry the surface completely, and reapply in a slow, continuous bead. For professional results, refer to ASTM C920-18(2024) application guidelines

Q3. Why does silicone sealant turn moldy in bathrooms?

Even “sanitary” silicone can develop mold if exposed to constant moisture and poor ventilation. Use a sanitary silicone sealant with fungicide additives and keep the area dry when possible. Regular cleaning with non-abrasive cleaners helps prolong life.

Q4. How long does silicone sealant take to cure fully?

Most silicones cure at 2–3 mm per day, but full curing can take up to 7–14 days, depending on bead thickness, humidity, and temperature. Always check manufacturer technical data sheets for exact curing times.

Q5. Can I apply new silicone over old silicone?

No. Old silicone must be completely removed because new sealant will not adhere properly. Use a sealant remover or mechanical scraper before reapplying.

Q6. Why is my cured silicone sealant cracking or shrinking?

This is often due to using the wrong type of sealant for high-movement joints or applying too thin a bead. For structural or expansion joints, choose a structrual silicone sealant that meets ISO 11600 movement capability standards.

Post time: Sep-18-2025